Mold assembly for making a magnetic base

ABSTRACT

There is disclosed a magnetic printing base for one or more printing plates, a method of making the magnetic base, and a mold in which moldable,non-magnetic adhesive material is molded about various parts of the magnetic base. The base is structured to permit magnetic circuit devices and end plates to be interconnected by the non-magnetic material into a unitary arrangement. Each magnetic circuit device includes a flat magnet disposed between and in ccontact with a pair of flat magnetizable plates. The permanent magnetsextend short of the finaldesired dimension of the base. The plates and the molded material initially extend beyond the final desired dimension of the base, but are trimmed off by a cutter to the final desired dimension after assembly of the base. To obviate the tendency of the printing plate to creep or drift, the spacing between the magnetic circuits is such that the strength, at surface of the base, of the magnetic flux field between next adjacent pole plates of adjacent magnetic circuit devices is equal to the strength, at the surface of the base, of the magnetic flux field between the pole plates of a magnetic circuit device itself.

United States Patent [191 Jenkins Feb. 11, 1975 Related US. ApplicationData [62] Division of Ser. No. 87,673, Nov. 9, 1970.

[52] [1.8. CI 249/95, 164/108, 249/96 [51] Int. Cl. 322d 19/00 [58]Field of Search 249/83, 84, 705, 171, 173, 249/175, 176, 177, 180, 184,I60, 163, 164. 122,123,124,129,143,144,151,108,165, 95, 96; 425/D1G. 33,DIG. 10; 164/109, 139,

[56] References Cited UNITED STATES PATENTS 1,407,569 2/1922 Pedersen249/164 X 1,915,488 6/1933 Gere 249/164 X 2,083,395 6/1937 Pfalzgraff249/95 X 3,058,156 10/1962 O'Connor 249/108 X 12/1967 Kolberg 249/151 XPrimary Examiner-Francis S. Husar Assistant Examiner-John S. BrownAttorney, Agent, or Firm--Joseph J. Grass [571 ABSTRACT There isdisclosed a magnetic printing base for one or more printing plates, amethod of making the magnetic base, and a mold in whichmoldable,nonmagnetic adhesive material is molded about various parts ofthe magnetic base. The base is structured to permit magnetic circuitdevices and end plates to be interconnected by the non-magnetic materialinto a unitary arrangement. Each magnetic circuit device includes a flatmagnet disposed between and in ccontact with a pair of flat magnetizableplates. The permanent magnetsextend short of the finaldesired dimensionof the base. The plates and the molded material initially extend beyondthe final desired dimension of the base, but are trimmed off by a cutterto the final desired dimension after assembly of the base. To obviatethe tendency of the printing plate to creep or drift, the spacingbetween the magnetic circuits is such that the strength, at surface ofthe base, of the magnetic flux field between next adjacent pole-platesof adjacent magnetic circuit devices is equal to the strength, at thesurface of the base, of the magnetic flux field between the pole platesof a magnetic circuit device itself.

11 Claims, 8 Drawing Figures MOLD ASSEMBLY FOR MAKING A MAGNETIC BASECROSS-REFERENCE TO RELATED APPLICATIONS This is a division ofapplication Ser. No. 87,673 filed Nov. 9, 1970, which is assigned to thesame assignee as the present application.

BACKGROUND OF THE INVENTION This invention relates to the art ofmagnetic printing bases, and methods of and molds for making same. Thereare numerous prior art patents relating to magnetic bases and the like;examples are US. Pat. Nos. l,657,287, 2,178,774, 2,481,191, 2,952,205,2,992,733, 3,024,392, 3,027,835, 3,039,390, 3,086,461, 3,097,598,3,180,259 and 3,509,819.

SUMMARY OF THE INVENTION The invention resides in a mold assembly formaking a low-cost, unitized magnetic base especially adapted for holdinga printing plate. Although the mold assembly is illustrated with acircular cylindrical roll, it is also applicable to a flat base of thetype disclosed in above mentioned US. Pat. Nos. 2,481,191 and 3,027,835.The mold for making the base of the invention is economical to constructhaving basically a pair of mold sections and end caps or plates. Themold sections have positioning means specifically in the form ofgrooves, formed at its inner surface. The end plates are clamped againstthe ends of the mold sections by means of tie rods which extend throughthe end plates externally of the mold sections. A nozzle disposed at thebottom of the mold distributes moldable material lengthwise of the moldcavity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of amagnetic base for printing plates;

FIG. 2 is a side elevational view, partly in section, of the magneticbase shown in FIG. 1;

FIG. 3 is a sectional view taken generally along line 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view showing a portion ofthe magnetic base as it appears during one of the manufacturing steps;

FIG. 5 is an exploded perspective view of a mold in which the magneticbase can be molded;

FIG. 6 is a vertical sectional view of the mold, showing the magneticbase in the mold after the moldable material has filled the mold;

FIG. 7 is a sectional view taken generally along line 77 of FIG. 6; and

FIG. 8 is a sectional view taken generally along line 88 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With particularreference to FIGS. 1, 2, and 3, there is shown a magnetic base in theform of a printing cylin der or drum generally indicated at 10 mountedon shaft 11. The base 10 can be secured to and driven by the shaft 11 orthe base 10 can be rotatable with respect to the shaft 1 and driven byother means, as desired. The magnetic base 10 is illustrated asincluding a plurality of spaced apart permanent magnetic circuit devicesgenerally indicated at 12. Each magnetic circuit device 12 includes aflat, annular, permanent magnet 13 and a pair of magnetizable poleplates 14. Each magnet has a central hole 13 and each plate 14 has acentral hole 14. A cylindrical mounting member 15 in the form of asleeve is shown to pass through the holes 13' and 14' and forms a fluxpath for each of the magnetic circuits. The plates 14 and the member 15are composed of magnetizable, easily machinable material such as lowcarbon steel. End plates 16 are received about reduced portions 17 ofthe mounting member 15 at locations spaced apart from the endmostmagnetic circuit devices 12. The magnetic circuit devices 12 are allconstructed with equal strength; the magnets 13 are of the same size andcomposition and the pole plates 14 are of the same size and composition.The magnets 13 are so arranged that alternate pole plates 14 are polednorth-south-north-south, and so on, in a direction longitudinally of thebase 10 as indicated by N and S in FIG. 2. Accordingly, the nextadjacent pole plates 14 of adjacent magnetic circuit devices 12 are ofopposite polarity. In accordance with the invention, the distancebetween adjacent magnetic circuit devices 12 is not arbitrary, butrather it is established by spacing the magnetic circuit devices 12apart by a distance at which the magnetic flux field strength betweennext adjacent pole plates 14 of adjacent magnetic circuit devices 12 areequal, or substantially so, to the magnetic flux field strength of themagnetic circuit devices 12 themselves. Once the spacing has beenestablished for a magnetic base having circuit devices of a particularsize, strength, material and configuration, any number of such bases canbe constructed using the same spacing.

The external diameters of the magnets 13 are less than the externaldiameter of the base 10 whereas the plates 14 extend all the way to thefinal surface of the magnetic base 10. Each of the plates 14 has fourequally spaced apart holes 18 near its periphery. The holes 18 extend atleast partly beyond the associated magnets 13. The end plates 16 havefour spaced apart apertures or holes 19 which are larger in diameterthan the holes 18 in the plates 14. Moldable, non-magnetic, adhesivematerial 20, such as epoxy fills: the space between the magnets 13 andthe surface of the base 10 between associated plates 14, the spacesbetween the outer surface of the cylinder member 15 and the outersurface of the base between plates 14 of adjacent magnetic circuitdevices 12, the spaces between the plates 14 of the endmost magneticcircuit devices and the associated end plates 16 between the cylindricalmember 15 and the surface of the base 10, and the holes 18 and 19 inrespective plates 18 and 19. The magnetic base 10 is accordingly formedinto a unitary support structure in which a magnetizable printing plateor a printing plate having a magnetizable holding portion is held to thebase 10 by magnetic attraction, and in addition, the plates 14 and thenon-magnetic material 20 serve to provide a solid support for theprinting plate or plates. To assure adequate keying of the material 20to the member 15, the outer surface of the member 15 between the nextadjacent plates 14 of adjacent magnetic circuit devices 12, and betweenthe plates of endmost circuits l2 and associated end plates 16 isroughened at annular zones 15. A fragmentary portion of one of thesezones 15' is shown in FIG. 6. Roughening can be accomplished by knurlingor any other suitable means.

With reference to FIGS. 1 and 3, printing plates P constructed at leastin part of magnetizable material are shown held onto the base bymagnetic attraction. The base 10 is shown to be provided with fourlongitudinally extending slots or grooves 21 in its periphery. The slots21 cut through the end plates 16, the non-magnetizable material 20, andthe plates 14. Leading edges of four of the printing plates are shown tobe received in the grooves 21 which prevents the printing plates P fromcreeping around the base 10 as its rotates during the printingoperation. The grooves 21 are preferably milled into the base 10 by amilling cutter (not shown).

With particular reference to FIG. 4, there is shown in exaggerated form,the manner in which plates 14 initially extend beyond the final desiredsurface S of the base 10. In the particular embodiment of a base 10 ofcylindrical form illustrated in the drawings, the plates 14 initiallyextend beyond the final desired surface S and in particular have alarger diameter than the final diameter of the base 10. It has beenfound to be most economical to eliminate close tolerances by sizing theplates 14 larger than necessary and allowing wide positive tolerances,and by sizing the magnets 13 smaller than necessary and allowing widetolerances. As one of the final steps in the manufacturing operation,the base 10 is turned on a lathe by rotating the base 10 in conventionalmanner relative to a cutter which moves at a predetermined rate of feedin a direction longitudinally with respect to the base 10, therebyremoving material 20 and the portions of the plates 14 radially beyondthe final desired surface S of the base 10.

With reference to FIGS. 5-8, there is shown a mold generally indicatedat 30 which is useful in performing the molding step of the invention.The mold 30 is shown to include a pair of mold sections 31 and 32 and apair of end plates 33 and 34. The mold sections 31 and 32 are curved andextend through arcs of about 170 each. The mold section 31 has sideedges 31 and 31", and the mold section 32 has side edges 32' and 32".When the mold is assembled side edges 31" and 32" of the respective moldsections 30 and 31 are in liquid-tight abutment with an elongated nozzle35, and there is a gap between the side edges 31' and 32 as best shownin FIGS. 7 and 8. A plurality of tie rods 36 cause the end plates 33 and34 to exert clamping pressure on the ends of the mold sections 31 and 32when nuts 37 are tightened.

Each of the mold sections 31 and 32 has a plurality of positioning andholding grooves 38 formed at its inside surface. These grooves 38 extendin an arcuate direction between the respective side edges 31' and 31"and 32 and 32". Assuming that a circular cylindrical printing base is tobe fabricated, a circular cylindrical member shown to take the form of asleeve is provided. Then plates 14 and magnets 13 can be assembled ontothe member 15 either individually or as sets or groups of magnetcircuits. In the illustrated embodiment, one magnetic circuit comprisesa permanent magnet 13 disposed between and in contact with a pair ofplates 14. If the magnetic circuits are to be assembled as sets theattractive force of the magnet 13 will hold the associated magnetizableplates 14 to it and hence each magnetic circuit is easily moved intoposition by sliding the magnetic circuit onto the member 15. In theillustrated embodiment the magnetic circuits 12 are shown to be spacedapart. As the magnets 13 have a diameter which is intentionally lessthan the final diameter of the base 10 and the plates 14 having adiameter greater than the final diameter of the base 10, the accuracy ofthe outer surface of the base 10 is not dependent upon accurate sizingor location of the holes 13 and 14'. Accordingly, holes 13 and 14' areacceptable even though larger than necessary by a considerabletolerance.

Endmost grooves 39 in the mold sections 31 and 32 are shown to receiveend plates 16. The grooves 38 have a width which is slightly greaterthan the combined thicknesses of two plates 14 and the magnet 13 so thatduring the molding operation the magnetic circuits 12 are not apt to bedisplaced by the moldable material. Here again accuracy of positioningthe magnetic circuits 12 is not necessary. With the components which areto comprise the base 10 disposed within the mold and the mold in theclamped condition as shown in FIG. 6, the moldable, non-magneticadhesive material is forced into the mold through orifices 35' in thenozzle 35. As the material enters the mold, air escapes through the gapbetween side edges 31' and 32' of the mold sections 31 and 32. As themagnets 13 and the associated plates 14 have flat sides, the moldablematerial does not flow between the contacting surfaces. However,material is able to flow into the spaces between plates 14 of adjacentmagnetic circuits 12, into the space around the magnets 13 and betweenthe associated plates 14, between the plates 14 of the endmost magneticcircuits 12 and the end plates 16, into and through holes 18 in theplates 14, and into holes 19 in the end plates 16, thereby providing aunitized base. As the moldable material, preferably in the form of epoxygradually fills the spaces described above until excess non-magneticmaterial flows into the gap between side edges 31 and 32' at the timeflow of additional material into the mold through the nozzle 35 isinterrupted and the moldable material is allowed to set and harden.After the material 20 sets and hardens, the mold 30 is removed withrespect to the base 10 and the base 10 is ready to be turned on a lathe.

lf desired, many of the benefits of this invention can be achieved byapplying the invention to a flat bed type of magnetic base. ln thatevent the final desired surface of the base 10 can be achieved by usinga milling cutter (not shown). The milling cutter would make passesrelative to the base 10 in the same direction as the direction in whichthe plate and magnets extend.

It is preferred to use one-piece magnets 13 although segmented magnetscan be employed, if desired, within the spirit of the invention.

Other embodiments and modifications of this invention will suggestthemselves to those skilled in the art, and all such of these as comewithin the spirit of this invention are included within its scope asbest defined by the appended claims.

1 claim:

1. A mold assembly for making a cylindrical magnetic base having acylindrical member and spaced apart magnetic circuit means disposed onthe cyclindrical member, said mold assembly comprising: mold sectionspositioned to provide a mold cavity, a pair of end plates disposed atopposite ends of the mold sections for closing off the ends of thecavity, means provided at the inner surface of at least one of the moldsections for locating the magnetic circuit means at predeterminedpositions lengthwise of the mold cavity, wherein the locating meanscomprises spaced apart grooves in at least the one mold section forreceiving the magnetic circuit means and holding them in spaced apartrelationship while the mold is being filled, means for holding the endplates and mold sections together, the cylindrical member and themagnetic circuit means being disposed in the cavity, and means includinga nozzle extending lengthwise of the mold cavity for introducingmoldable material into the mold cavity around the cylindrical member andthe magnetic circuit means.

2. A mold assembly as defined in claim 1,wherein the end plates arepositioned to exert clamping forces against the ends of the moldsections, and means for exerting clamping force against the end platesto hold the mold sections together.

3. A mold assembly as defined in clalim 1, wherein the holding meanscomprises a plurality of tie rods.

4. A mold as defined in claim 1, wherein the end plates receive the endportions of the mold sections.

5. A mold assembly as defined in claim 1, wherein the nozzle extendssubstantially throughout the length of the mold cavity, the nozzlehaving a plurality of orifices.

6. A mold assembly as defined in claim 1, wherein the nozzle is disposedin the lower region of the mold cavity between adjacent mold sections,and an air vent in the upper region of the mold cavity.

7. A mold assembly as defined in claim 1, wherein the nozzle is disposedin liquid-tight relationship between the two mold sections.

8. A mold assembly for making a cylindrical magnetic base having acylindrical member and spaced apart magnetic circuit means disposed onthe cylindrical member, said mold assembly comprising: a pair ofgenerally semi-circular mold sections positioned to provide a generallycircular mold cavity, a pair of end plates disposed at opposite ends ofthe mold sections for closing off the ends of the cavity, thecylindrical member and the magnetic circuit means being disposed in thecavity, means provided at the inner surface of at least one of the moldsections for locating and holding the magnetic circuit means atpredetermined spaced apart positions lengthwise of the mold cavity,means for holding the end plates and mold sections together. and anozzle having means for distributing moldable material alongsubstantially the entire length of the mold cavity, said nozzle being inliquid-tight relationship with the mold sections along the lengths ofmold sections.

9. A mold assembly as defined in claim 8, wherein the end plates receivethe end portions of the mold sections.

10. A mold assembly as defined in claim 9, wherein the ends of the moldsections are received in the end plates, and means for releasablyclamping the end plates against the ends of the mold sections.

11. A mold assembly as defined in claim 8, wherein the nozzle isdisposed between the two mold sections. {F k UNITED STATES PATENT ANDTRADEMARK FFICE CERTIFICATE CF (IQECTEN PATENT NO. 3,865,343

DATED February ll 1975 N Q) William A. Jenkins It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Assignee: "Monarch Marking System Company" should be -Monarch MarkingSystems, Inc.. In the Abstract, line 9, "contact" is misspelled;

Column 1, line 64, "1" should be l0-. Column 3, line 5,"non-magnetizable" should be non-magnetic-. Column 6, line 22, "9"should be 8-.

Signed and Sealed this fourteenth Day of October 1975 [SEAL] Arrest.

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflarentsand Trademarks

1. A mold assembly for making a cylindrical magnetic base having acylindrical member and spaced apart magnetic circuit means disposed onthe cyclindrical member, said mold assembly comprising: mold sectionspositioned to provide a mold cavity, a pair of end plates disposed atopposite ends of the mold sections for closing off the ends of thecavity, means provided at the inner surface of at least one of the moldsections for locating the magnetic circuit means at predeterminedpositions lengthwise of the mold cavity, wherein the locating meanscomprises spaced apart grooves in at least the one mold section forreceiving the magnetic circuit means and holding them in spaced apartrelationship while the mold is being filled, means for holding the endplates and mold sections together, the cylindrical member and themagnetic circuit means being disposed in the cavity, and means includinga nozzle extending lengthwise of the mold cavity for introducingmoldable material into the mold cavity around the cylindrical member andthe magnetic circuit means.
 2. A mold assembly as defined in claim 1,wherein the end plates are posiTioned to exert clamping forces againstthe ends of the mold sections, and means for exerting clamping forceagainst the end plates to hold the mold sections together.
 3. A moldassembly as defined in clalim 1, wherein the holding means comprises aplurality of tie rods.
 4. A mold as defined in claim 1, wherein the endplates receive the end portions of the mold sections.
 5. A mold assemblyas defined in claim 1, wherein the nozzle extends substantiallythroughout the length of the mold cavity, the nozzle having a pluralityof orifices.
 6. A mold assembly as defined in claim 1, wherein thenozzle is disposed in the lower region of the mold cavity betweenadjacent mold sections, and an air vent in the upper region of the moldcavity.
 7. A mold assembly as defined in claim 1, wherein the nozzle isdisposed in liquid-tight relationship between the two mold sections. 8.A mold assembly for making a cylindrical magnetic base having acylindrical member and spaced apart magnetic circuit means disposed onthe cylindrical member, said mold assembly comprising: a pair ofgenerally semi-circular mold sections positioned to provide a generallycircular mold cavity, a pair of end plates disposed at opposite ends ofthe mold sections for closing off the ends of the cavity, thecylindrical member and the magnetic circuit means being disposed in thecavity, means provided at the inner surface of at least one of the moldsections for locating and holding the magnetic circuit means atpredetermined spaced apart positions lengthwise of the mold cavity,means for holding the end plates and mold sections together, and anozzle having means for distributing moldable material alongsubstantially the entire length of the mold cavity, said nozzle being inliquid-tight relationship with the mold sections along the lengths ofmold sections.
 9. A mold assembly as defined in claim 8, wherein the endplates receive the end portions of the mold sections.
 10. A moldassembly as defined in claim 9, wherein the ends of the mold sectionsare received in the end plates, and means for releasably clamping theend plates against the ends of the mold sections.
 11. A mold assembly asdefined in claim 8, wherein the nozzle is disposed between the two moldsections.